The present exemplary embodiments relate to filter apparatus including industrial filters, replaceable filter leafs for use therewith, and methods of using same. They find particular application in connection with polishing filters and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiments are also amenable to other like applications.
Filtration is a common operation performed in process plants and in other industries. One of the many design considerations in the filtration art is the amount of filtration area that can be made available in a given space and cost. On one hand, a large filtration area is preferred because a larger filtration area results in higher filtration rates. Further, large filtration areas reduce or minimize the number of cleaning cycles required for a given volume of filtered material. However, on the other hand, additional considerations such as accessibility and economics motivate designs that are not specifically optimized solely for filtration area as a design parameter.
Essentially, basic filtration is accomplished by passing a fluid such as a liquid or gas bearing solids through a porous media, usually a cloth, paper, sieve, or other structure. Solid particles carried by the fluid are separated from the fluid by the filter media as the fluid passes therethrough.
Many factors influence a determination of filter design. One primary factor of filter design, however, is the degree to which solids being filtered from the fluid can be accumulated onto and, thereafter, removed from the media. At one extreme of design consideration, particles are easily filtered. There, a first filter layer is substantially permeable to the liquid or gas filtrate and permits subsequent layers to be filtered until a substantial cake of deposited particles is formed, at times up to one half inch thick or more. Cake removal usually leaves behind a clean filter media which can then be reused many times. Filters of this type are typically referred to as “process filters” and are used for applications where a cake can be built up onto the media and thereafter removed for reuse of the media several times. Examples include filter presses, leaf filters, drum filters, belt filters, and disc filters. In these cases, maximizing filtration area and providing for solids removal are major design considerations.
On the other extreme of filter design parameter consideration, the filtered particles themselves are small, irregularly shaped, or deformable. They embed themselves into the media and cannot be removed. The used media must therefore be disposed of and replaced with new media. Filters of this type are generally referred to as “polishing filters” and are used with these applications. Polishing filters are designed for ease of media replacement and, to that end, typically include cartridge filters and popular bag filters.
In addition to the above, overall, economics plays a role in filter design, construction, and use. Generally, in process filtration, the solids separated from the filtrate are either a product or a significant by-product of a process around which a business is built. Accordingly, these filters have evolved to large proportions, typically 200 square feet filtration area or more and usually include some level of automation for separation of the filtered solids from the filter apparatus and for handling and subsequent processing thereafter. Furthermore, other parts of the process are specifically arranged to generate suitable solids for cake filtration necessary for high volume. Filters of this type are thus an integral component in the process and as would be expected, a substantial capital investment for the business.
In contrast, polishing filters are typically used to remove incidental or other unwanted solids from a moving liquid or other fluid stream. The main purpose of polishing filter is to keep the filtrate clean for maintenance purposes, product appearance purposes, or where a high purity in the moving fluid is necessary. One example of an application where a polishing filter would be useful is in a closed loop cooling water system. Typical polishing filters handle a very low volume of solids and are usually small i.e. less than 20 square feet of filtration area and are inexpensive. Therefore, they are considered to be an ancillary part of the overall manufacturing or process system. Usually, therefore, it would be uneconomical to use a solids preparation step and a process filter in a polishing filter application.
A problem arises, however, when a polishing filter is placed in a situation to handle more than a small volume of solids. The typical solution is often the installation of several bag or cartridge filters in parallel. However, this solution increases the cost by adding additional equipment and manpower.
Although there have been attempts to increase the filtration area in bag and cartridge filters, one fundamental problem remains in that both the housings and replacement elements for both types of filters are typically cylindrical in shape. The cylindrical shape provides for a simple design and gives the components additional strength against the pressure of filtration and permits easy replacement of the elements. However, cylindrical filters limit the filtration area for a given filter apparatus volume.
According to the above, therefore, there is a need in the art for a leaf filter apparatus useful in applications where heretofore polishing filters were utilized. The leaf filter apparatus should be physically overall small, inexpensive, yet capable of filtering a substantial volume of incidental or unwanted solids from a moving fluid. Additionally, the filter leafs are preferably made of a disposable material and are easily detachable from the filter apparatus structure.